[tex] \frac{6*10*sinA}{2}=15 \sqrt{3 } \\ \frac{60sinA}{2} =15 \sqrt{3} \\ 30sinA =15 \sqrt{3};sinA= \frac{ \sqrt{3} }{2} \\ cosA= \sqrt{1-( \frac{ \sqrt{3} }{2})^2 } = \sqrt{ \frac{1}{4} }= \frac{1}{2} \\ BC^{2}= AB^{2}+ AC^{2}-2AB*AC*cosA \\ BC^{2}=36+100-2*6*10* \frac{1}{2} \\ BC^2=136-60=76 \\ BC= \sqrt{76} cm[/tex]